<?php 
  session_start();  
?>
<html>
<body> 
<?php
            $bmi = $_SESSION['vaha'] / ($_SESSION['vyska'] *$_SESSION['vyska']);
            $_SESSION['bmi']=$bmi;
echo "<meta http-equiv='refresh' content='1;url=krok4.php'>";	   	    

?> 
</body>
</html> 